Impulse-repeating electromagnetic relay



Sept. 21, 1954 J. l. BELLAMY 2,689,883

IMPULSE-REPEATING ELECTROMAGNETIC RELAY Filed Oct. 12, 1951 RIG. 1

44 45 43 4042 I 4| 25 9 37 47 33" i r al INVENTQR M a. WWW

Patented Sept. 21, 1954 IMPULSE-REPEATING ELECTROMAGNETIC RELAY John I.Bellamy, Wh-eaton, Ill., assignor, by mesne assignments, toInternational Telephone and Telegraph Corporation, a corporation ofMaryland Application ctober12, 1951, Serial No. 250,974

4 Claims. 1 This invention relates to animpulse-repeatingelectromagnetic relay, and it primary object is to provide a relay ofthat kind which will respond with improved faithfulness over a Widerange of.

series and shunt resistance conditions of the signal line over which theimpulses are received.

Thisapplication is a continuation in part of my prior application forElectromagnetic Relays, Serial Number 687,629, filed August 1, 1946.

GENERAL DESCRIPTION A simple, reliable, and economical form'ofelectromagnetic relay widely used in telephone switchboards and inrelated fields is based on a U-shaped magnet structure, made up. of an.L- shaped magnetic return plate and an electromagnet which lies parallelto the longer arm of the return plate, with one end secured to theshorter arm. An armature, mounted on the free end of the return plateand attractable to the electromagnet upon energization thereof, controlsone or more sets of contact bladesmounted on the return plate.. Amongother uses, such a relay is used as a. a line relay to repeatdirect-current control impulses into local circuits.

Reference is made to Telephony, Including Automatic Switching, by Smith;Frederick. J. Drake and Co., 1924. Figure 203 of that publication. showsa line relay LR of a selector switch and of a connector switchcontrolled successively by series of impulses received over a line fromacalling telephone. Adjustment of Automatic Apparatus, startin on page3'71 of that publication, points outthatthe pulsing mechanism of thetelephone calling device is adjusted to give a normal impulse speed(frequency) of about ten per second; that a ratio of'about 65 percentbreak of the impulse contacts is common; andthat, in one example, theextreme test limits of the line-resistance range over which a line relaycan successfully repeat the impulses at a rate of fourteen per second(see paraditions, comprising, (1) a line of-minimum line resistance, butwithpoor insulation and conseqnent high line leakage, and (2) a line ofmaximum line resistance, but with good insulation "and consequent lowline leakage. As the noted Chapter XXIII; Testing and 'tacts.

publication makes clear, a line relay adjusted to meet both extremesoperates early and restores late under the first extreme condition,while it operates late and restores early under the second extremecondition. On analysis, this appears to be the necessary consequence ofa relay of the noted character, wherein the armature is acted upon by anelectromagnet which supplies a variable operating force in but a singledirection, and is opposed by the fixed restoring-spring load of thecontact-blade assembly.

For the first noted extreme condition (a line of minimum seriesresistance and maximumleakage), the armature of a relay having a correctbasic adjustment (armature stroke and residual air gap) requires a heavyrestoring force to insure that it restores with reasonable promptnesswhen the line is opened at the impulse con- The magnetic structure ofthe relay is then at its highest point of magnetic saturation, andthehigh magnetic energy tends to dissipate slowly because of the shadingeffect of the low shunt resistance. Moreover, eddy currents and theresidual tendencies present in the magnetic structure tend to cause thearmature of a highly saturated relay of this type to restore late unlessthe restoring spring force is substantial.

When the same relay, soadjusted and with the noted necessarily heavyrestoring-spring load, is used for the second noted extreme condition (aline of maximum series resistance and negligible leakage), the armaturerestores more quickly because the flux level of the magnetic structureis, much lower. This action, coupled with the fact that the high seriesresistance causes the armature to operate much later on the closure ofthe impulse contacts, causes a very'large change in the break-make ratioof the repeated impulses. In practice, the restoring-spring force is soregulated that the departure from the most desirable-ratio is sharedabout equally between the two extremes of line conditions. Then the mostdesirable break-make ratio of the repeated pulsesoccurs when theconnected line has a combination of series and shunt resistances fallingabout member in the form of a branch pole member having a shading devicethereon. The branch pole member acts upon the armature in opposition tothe normal tractive pole member, whereby the armature is operated by themain, unshaded pole member at the beginning of an impulse, and restoredby the action of the auxiliary, shaded pole member at the terminationthereof. By this arrangement, (1) the range of line conditions overwhich the relay can repeat impulses of tolerable ratio is increased, and(2) the impulses repeated by the relay over the extreme range of knownrelays are of a comparatively uniform break-make ratio.

Other objects and features will appear as the description progresses.

The drawings Referring now to the drawings, comprising Figs. 1 to 6,

Figs. 1 to 3 show respectively a side, top, and front view of relay RI,comprising the preferred embodiment;

Fig. 4 shows a partial side view of relay R2, comprising a desirablemodification of relay RI of Figs. 1 to 3;

Fig. 5 shows a typical circuit use of relay R| (Figs. 1 to 3); and

Fig. 6 shows a modification of Fig. 5 which uses relay R2 (Fig. 4).

Preferred embodiment (Figs. 1 to 3) Referring now to Figs. 1 to 3, relayRI, the preferred embodiment, includes an L-shaped magnetic return plate2, having the core 6 of the electromagnet fixed thereto by screw 1.Spoolheads 1 and 9 are fixed with core 3 to define a space for windings3, separated by washer 50. Four winding terminals I!) are fixed withspoolhead 9. The spoolheads ii and 9 are preferably of a similarhalf-circular and half-square shape, as shown for the spoolhead 8 inFig. 3. The circular half of spoolhead 9 is uppermost, While the squarehalf of spoolhead 8 is uppermost, providing a sturdy surface whichrigidly supports the front end of member 2 and holds the electromagnetagainst rotation.

Armature 5 is supported on pivot rod I8, which passes through ears 2| ofthe armature and ears ll of bracket [5, secured to member 2 by screwsH5. Bracket I5 is preferably of magnetic ma terial to provide acomparatively large area of return air gap between armature 5 and partl5, and thence through member 2. Strip IQ, of nonmagnetic material, issecured to part l5, as by rivets 20, to act as a front stop for armature5 in its forward motion toward the main, tractive pole member 4.

The contact mechanism of the relay is contained in assembly of Figs. 1and 2, including clamp plates 34 and 43, secured together by clampscrews 44, and retained on member 2 by screws 45.

The contact assembly includes two columns, 3| and 32, of contact blades.Each column includes a lower fixed contact blade 31, an intermediate,traveling contact blade 39, and an upper, fixed contact blade 4 Thefixed contact blades 31 and 4| are preferably of substantially greaterthickness than the traveling contact blade 39, the thickness of which isaccentuated in the drawing to avoid crowding of the lines.

Actuation of the contact mechanism is accomplished by the T-shaped reararm 22 of the armature 5, through the medium of the relatively 4. thinactuating blade 35 and the overlying insulating actuator 41.

The fixed contact blades 3'! and 4| are each provided with windows 48(Fig. 2), to permit actuator 41 to move freely therethrough. Eachcontact blade has a rear terminal portion 33 for the attachment of aconductor thereto. The contact blades are maintained insulated from eachother and from the clamp plates 34 and 43 by insulating plates 36, 38,40, and 42.

The normal position of armature 5 is determined by back-stop arm 23,which rests on the nonmagnetic plate 25, retained in position beneaththe assembly 3!).

Bending of actuating arm 22 of the armature to bring the movable contactelements to the desired position (with armature 5 fully operated andresting against stop member I3) as well as the bending of back-stop arm23 to determine the normal position of armature 5, is facilitated byslots 24 through the arms 22 and 23 for receiving a suitable adjustmenttool.

Movement of armature 5 responsive to energization and deenergization ofthe windings 3 is controlled jointly by the main, actuating pole member4 and the auxiliary, restoring pole member 5|. Member 5| is encircled bya conducting shading device 52, composed of a desired number oflaminations of a conducting material such as copper.

Pole members 4 and 5| are secured to the front end of core 6 by screwII, which passes through enlarged or vertically slotted openings inparts 4 and 5| to permit vertical adjustment of these i parts before thefinal tightening of screw II.

For most uses of the relay, the tractive face of pole member 4 is asubstantial distance below the upper face of front stop member Is, toleave a substantial residual air gap between parts 4 and 5 with thearmature 5 in its operated position, and part 5| is suiliciently highthat about the same air gap normally exists betwen it and the uppersurface of armature 5. It will be understood that armature 5 ismaintained in that position in the illustrated embodiment by therelatively light spring load imposed by parts 39 and 35.

When a substantial current flow occurs in windings 3, pole members 4 and5| are both magnetized and each attracts armature 5. Conducting shadingmember 52, however, delays the passage of flux through member 5|, withthe result that armature 5 is effectively attracted by member 4 andmoves to operated position against the upper-face of stop-member l9before the flux through pole member 5| can reach an effectiverestraining value. Incidental to this armature movement, actuating arm22 raises actuating spring members 35 to thereby raise actuators 41.Contact blade 3| of each column (3|, 32) is thereby lifted out ofengagement with its fixed contact member 31, and is brought intoeffective engagement with its fixed contact member 4|.

When the current flow through the windings 3 is subsequently terminated,pole members 4 and 5| are consequently demagnetized, but thedemagnetization of pole member 5| is delayed by the shading action ofmember 52, with the result that armature 5 is thereby attracted to itsillustrated restored position, in aid of the restoring force exerted byspring members 35 and 39.

Reversed-action embodiment (Fig. 4)

Referring now to Fig. 4, the relay R2 shown therein is exactly similarto the relay RI of Figs. 1 to 3 except that Shading member 52 has beenshifted from restoring pole member I to actuating pole member 4.

When the windings 3 of relay R2 are energized to magnetize pole members4 and 5I, member 5| becomes magnetized immediately, while the passage offlux through pole member 4 is delayed by the action of the conductingshading member 52. As a result, armature 5 remains in normal position.

When the current flow through the windings of relay R2 is discontinued,pole member 5I demagnetizes with comparative promptness, while shadingmember 52 delays the demagnetization of pole member 4 for an interval.During this interval, armature 5 is operated by member 4. If thewindings remain currentless until the effect of shading member 52 hasdied away, armature 5 is then restored by spring action.

In the normal intended use of relay R2, hereinafter described, theestablishment of current flow through the windings of the relay isfollowed by a series of impulses in the form of momentary currentinterruptions. As a consequence, the armature of the relay is attractedto pole member 4 upon the first interruption and remains so attracteduntil the current flow is resumed, whereupon it is magnetically restoredby the overpowering action of pole member 5|, remaining thus restoreduntil the next interruption occurs.

Circuit use of relay R1 (Fig. 5)

Referring now to Fig. 5, a simplified typical contemplated use of therelay R! of Figs. 1 to 3 will be described.

506 represents the control station, which may comprise a dial telephone,with 5") representing the normally open hookswitch contacts and 5representing the impulse contacts of the dial calling device. Conductors5I2 are the usual line conductors in a two-wire signalling system, suchas the conductors of a dial telephone line. LS represents a partiallyillustrated line switch of the type indicated in Fig. 203 (opposite page268) of the cited publication, the arrangement being such that any oneof a number of lines such as 5I2 can be switched into connection withthe relay RI. Each lineswitch LS may have access to a number of thedigit recording circuits, and each such circuit may be accessible to anumber of lineswitches LS. The symbols 5 I I indicate multipleconnections to the contact banks of other lineswitches LS.

Relay RI (of Figs. 1 to 3) cooperates with the associated hold relay 52Iin controlling a stepping switch SSI. In a dial telephone system, thestepping switch is used to extend the conductors of a calling line to,or toward, the conductors of a called line, but for simplicity ofdisclosure the switch SS is illustrated as controlling the lighting ofdisplay lamps 550.

Stepping switch SS includes a brush 521 having the illustrated normalposition and having ten oif-normal positions in which it engages itsassociated contacts 1 to 1c respectively.

It is advanced by stepping magnet 523, and is returned to normal by theusual restoring spring (not shown) upon the operation of release magnet526.

Station 500 may be at some distance from the apparatus controlledtherefrom, or it may be a station comparatively close to the apparatus.The resistors 5I3 and 5M represent the distributed wire resistance ofthe line 5I2, and resistors 5I5 and 5 I 6 represent distributed leakagebetween the wires of the line, such as may result from wet, broken, ormissing insulators; contact between bare line wires and tree branches;or moisture in a cable.

Parts 8, fl, and 22 may each have a 1-inch width; core 6 may be threeeighths inch in diameter; and the other parts may be generally inproportion according to the scale used in the drawing. With thisproportioning, each of the windings 3 may comprise about 4000 turns ofNo. 34 enameled copper wire, having a resistance of approximately 200ohms. With a battery of about 50 volts, such as is commonly used in thecentral exchange of a dial telephone system, the relay RI has been foundto repeat dial impulses satisfactorily, without change of adjustment,over lines 5I2 ranging from substantially zero to 1800 ohms seriesresistance, represented by resistors 5I3 and 5M on the drawing, and withleakage (shunt resistance) ranging between infinity and 3600 ohms,represented by resistors 5 I 5 and SIB.

Operation of Fig. 5

When digit information is to be transmitted from station 500 of Fig. 5,hookswitch contacts 5H3 are first closed; impulse sending contacts 5I Iare then caused to open momentaril a number of times to deliver a seriesof break impulses over the line M2; and hookswitch contacts {Sill arelater opened when the transmitted registration is to be cleared out.

Upon the closin of hookswitch contacts 5I0, and if the lineswitch LS iscontrolled as is the one shown in Figure 283 of the cited publication,the usual operations of switch LS occur to extend the calling line 5I2to an idle circuit such as the one illustrated. Ehereupon, the twowindings 3 of line relay RI are energized in series over line 5I2, bycurrent supplied from the ungrounded negative pole of a grounded currentsource (not shown) assumed to be of approximately 50 volts in accordancewith the usual signalling and dial-telephone practice.

As the current rises in the windings 3 of relay RI, there is an in-phaserise of flux through pole member 4 of Fig. 1, and a much slower rise offlux through pole member 5! because of the retarding action of shadingmember 572. As a consequence, a greater tractive force is exerted onarmature 5 by the pole member 2 than is then exerted by the shaded polemember 5i. Armature 5 therefore moves promptly into engagement with itsfront-stop member It, being then nearer to member 4 than to member 5|.By the armature movement, contact blade I9 is moved away from member 31and into engagement with member 4 I, as previously described. Theengagement of parts 39 and EI closes a circuit for hold relay 52 I,which relay thereupon operates. At its contact arm 528, it disconnectscontact member 3? from the release wire 524 and connects it to thestepping wire 522, in preparation for transmission of impulses tostepping magnet 523.

On each momentary interruption of the line current incident to the notedoperation of impulse-sending contacts EI I (as upon the restoration ofthe usual telephone calling dial) armature 5 of the relay RI is promptlyrestored, the action being enhanced, as previously noted, by the promptcessation of flux in pole member 5 as compared to the flux in polemember 5!, which persists by virtue of the retarding action of shadingmember 52.

At the end of each momentary interruption impulse, the resumption ofnormal current flow 7 through thewindings 3 of relay RI causes armature5. of the relayto reoperate as described for the initial closure of theline circuit.

On each restoration of relay RI, the circuit of hold relay 52! is openedat contact blades 39 and 4!, but relay 52! remains operated during theseries of impulses because of its slow-releasing, as by having theindicated copper sleeve surrounding its core, between the core and thewinding, as is commonpractice in the art. As a result, relay 52 Iremains operated continuously throughout the transmission of a series ofimpulses.

On each momentary restoration of line relay RI, with hold relay 52!remaining operated, an impulse of current is transmitted to steppingmagnet 523 over wire 522, through contact members 39 and 31, and thefront contact of member 528. Stepping magnet 523 responds by advancingwiper 52! one step for each impulse received, engaging a separate one ofitscontacts 1 to 10 on each step. Since wiper 52'! is grounded, thelamps 1 to 10 in group 550 are momentarily lighted successively duringthe receipt of impulses. The lamp which corresponds to the contact onwhich member 52'! stands at the end of the series of, impulses remainslighted as a display signal of the value of the digit transmitted andregistered.

Off-normal contacts 525 become closed on the firststep of wiper 521.

When the registration is to be cleared out, hookswitch contacts 5 I areagain opened and are allowed to remain open. When this occurs, linerelay RI restores and remains restored, hold relay 52 I restoringshortly thereafter.

During the interval required for relay. 52! to restore following therestoration of relay RI, an additional, and somewhat prolonged, impulseis transmitted over wire 522 to stepping magnet 523. Wiper 52! isthereby advanced to the next contact, extinguishing the lamp previouslylit as a display signal, and lighting the next succeeding lamp. Ifdesired, this action can be avoided by adding one or more controlrelays, as is done in the signalling art.

When hold relay 52! restores, the circuit of stepping magnet 523 isopened, and a circuit is closed for release magnet 52%, from ground atcontact blade 39, through contact blade 37, back contact 528, andoiT-normal contacts 525. Theresulting operation of release magnet 526causes brush 521 to be restored to its illustrated normal condition.Off-normal contacts 525 now open the circuit of release magnet 526,leaving the circuit of Fig. in its illustrated normal condition.

Reversed-action embodiment (Figs. 4 and 6) Referring now to Fig. 6, theuse of the reversedaction relay R2 of Fig. 4 in a typical circuitarrangement will be described.

Fig. 6 is like Fig. 5 except that relay R2 is substituted for relay RI,and the associated control circuit is revised accordingly. Relay R2,because of its described reversed action, does not require a normallyclosed contactmember such as 3'! of Fig. 5. Instead, it uses two pairsof normally open contact members 39 and 4!, termed 39R, MR, and 39L, 4|Lin the respective columns 3! and 32 of Fig. 2.

Upon the closure of a circuit for relay R2, as over the line 5 I 2 of 5,the current builds up in the windings 3 of relay R2, but no movement ofthe armature (5) thereof occurs for reasons herebefore given, whereforethe contact members of the relay remain in their illustrated normal opencondition.

Upon each momentary interruption of the line, as at impulse contacts 5!I, the resulting cessation of current flow in the windings 3 of therelay R2 causes the armature (5) to be operated by the delayed action ofpole member 4, bringing the The armature of relay R2 comes to rest inits illustrated restored condition when the line remains closed at theend of the transmission of the series of interruptions impulses, leavingthe contact members of Fig. 6 in their illustrated open condition.

Upon each noted momentary closure of the contactmembers of relay R2, acircuit is momentarily closed by contacts 39R and 4 IR, over impulsewire 622, through contacts 628, for stepping magnet 623. By the actionof magnet 623, wiper 62'! is advanced step-by-step over its associatedcontacts to light a desired lamp 650.

As a further result of each momentary closure of the contacts of relayR2, contacts 3.9L and 4 IL close a circuit over wire 624 for releasemagnet 526. Release magnet 526, as is indicated by the notation "S. 0.,is a slow-operating electromagnet, preferably being so arranged byhaving a winding of considerable inductance and having the usualarmature-restoring spring (not shown) adjusted to apply substantialrestraining tension. As a consequence, release magnet 626 does notrespond to any of the momentary impulses delivered to it along with, andincidental to, the noted delivery of stepping impulses to magnet 623.

When the, display lighting of one of the lamps 1 to 10 in group 550 hasserved its purpose, the opening of the calling line, as at hookswitchcontacts 5H3, causes a cessation of line current. Thereupon relay R2 isoperated to close its contact members as previously explained. Sincethe. line current is not resumed at this time, armature 5 soon restores,at the end of asubstantial fraction of a second for example.

During the interval when relay R2 is operated following the notedopeningof the calling line,

release magnet 625 operates because the length of the impulse thendeliveredthereto over wire 624 exceeds the slow-operate period of themagnet. Upon operating magnet 626open-circuits stepping magnet 623 atits contacts 628. Magnet 626 remains operated, and wiper 621 is therebyrestored to its illustrated normal position. Release magnet 626 soonbecomes deenergized, upon the previously noted restoration of relay R2when. the current in shading member 52 of'Fig. 4 diesout. The apparatusof Fig. 6 is thus again in its illustrated normalcondition.

Performance considerations the design-o1" the relay and the adjustmentthereof.

One important design consideration is armature lightness. The armatureshould be relativelylight (having a small effective mass, or-

moment of inertia) compared to the available operating force, wherebythat force provides a high acceleration according to the general formulathat acceleration equals the force divided by the mass (A= /M). Then,the movement of the armature from either of its stop positions to theother can occur readily within the short interval allowable for suchmovement. In this respect, the armature 'can very likely be improved bynarrowing its width forward of the screws [6 (see Fig. 2), and bycorrespondingly narrowing the width of pole members :3 and iii,accompanied if necessary by an increase in the thickness of the polemembers. Lightness of armature 5 is further promoted by constructing itof a magnetic material having maximum permeability and having a highsaturation value, whereby its cross-sectional area can becorrespondingly reduced.

In the illustrated embodiment, however, the armature 5 has not beenspecially shaped for maximum lightness, nor has the use of a magneticmaterial better than commercially available annealed ingot iron sheet(about one sixteenth inch thickness) been found necessary for thesuccessful use of the relay under the conditions hereinbefore described.Annealed ingot iron is satisfactory for the remaining magnetic items,and soft cold-rolled steel has been used successfully for these items.Whatever the arma ture shape or material, best results are obtained whenthe armature itself comprises the most restricted portion (highestreluctance per 'unit length) of the magnetic circuit, and comprises theportion of the circuit which first reaches saturation when the windings3 develop sufficient magneto-motive force.

For the most favorable response over a given range of operatingconditions, the armature should have a short stroke. That is, the relayshould be so adjusted that the normal position and the operated positionof armature 5 are as close together as the demands of the contactmembers (Bl, 39, M) reasonably permit. This arises from the fact thatthe joint control exercised by the pole members 4 and El (in operatingthe armature 5 positively in each of the two directions of movement asthe force differential shifts in direction) is best exercised when thearmature is never so much closer to one pole member than to the otherthat the nearer pole unduy restrains the armature from starting itstravel toward the distant pole. In all forms of the device whichapplicant has constructed and tested, the operating range is verylimited if the stop positions are such that the armature comes intocontact with either pole member, and particularly the unshaded polemember. With the armature contacting a pole member, it is very difficultto adjust the device so that the armature will move to the other polemember unless the pole members are brought much closer together than thedrawings indicate. The armature stroke then becomes so small that theresulting movement is less than the requirements of the illustrated typeof contact members.

The shading efjectiveness of shading member 52 may vary between ratherwide limits, such from 506 to lGGU mhos for the circuit use illus tratedin Figures 5 and 6. Considerably higher conductance valuesof the shadingdevice can be used for interruption impulses of ten per second, so longas the line current and the flux through the shaded pole member haveboth reached substantially a steady-state condition before the starts,and for low-frequency interruption-im pulse situations wherein theinitial interruption closely follows the initial line closure, bestresults are obtained with the illustrated structure when the conductanceof shading member 52 does not exceed 500 mhos. Under the notedcircumstance, of only a very fleeting impulse, the passage of fluxthrough the shaded pole member is so retarded by a shading device ofhigh conductance that the energy stored in the shaded pole member isinsufficient to cause the armature to be urged toward that pole memberwith suflicient vigor when the current flow in interrupted.

Applicant is aware that certain prior structures, including thedisclosures in certain references of record in his prior patentapplication hereinbefore identified, have employed an armaturecontrolled jointly by an unshaded pole member and an opposed shaded polemember, but no such prior structure, so far as applicant is aware, iscapable of attracting its armature in one direction from a firstposition to a second position responsive to each flow (or sharp rise) ofdirect current, and of attracting the armature back to its firstposition responsive to each cessation (or sharp drop) in direct current.In making the foregoing statement, applicant takes the position that anyhalf cycle of alternating current, considered alone, comprises adirect-current impulse that rises to full value and ceases during theperiod of the half cycle of current.

The several factors governing the ability of a structure of thedisclosed character to operate the armature as hereinbefore describedinclud the following:

1. Armature lightness and bias, which govern the ease with which the netmagneto-tractive force, available incidental to a rise or a fall incurrent, can move the armature from its presently occupied position toits other position;

2. Armature sensitivity to flux differential, which is governed by thedistance by which the armature in either stop position, is separatedfrom the nearer tractive pole face as compared to its distance ofseparation from the other tractive pole face;

3. Total flux range, which is limited by the amount of flux whichsubstantially saturates the structure; and

4. Amount of shading or the conductance of shading member, whichdetermines, for any rate of change of total flux, the distribution ofsuch rate of change between the two pole members.

When a device of the disclosed-character has the foregoing factorsfavorably related according to the description hereinbefore given, itoperates in the described useful manner. Eut, when one or more of thefactors is too far out of proportion with the others, the device cannotperform according to the invention. For example, if the shadingconductance is too low compared to the flux range and to the armaturelightness and sensitivity, the armature cannot change positionsresponsive to any single impulse of direct current, or half cycle ofalternating current, of any strength or sharpness of rise or fall. Ifthe rise or fall be comparatively gradual, then the flux change isgradual, and the flux differential. is insufficient to generate a netforce differential great enough to withdraw the armature from its nearerpole member. On the other hand, if the rise or fall of current beabrupt, the flux. change is abrupt, but its duration and range are socur-- tailed by the flux range of the structure, that any resulting netmagneto-tractive force is too fleeting to attract the armature away fromthe nearer pole and move it-to its stop position closer to the otherpole. On repeated tests, a device so misproport'ioned responded to60-cyc1e alternating current even though it would not respond toanydirect-current pulses oi any magnitude or rate of change. A partialexplanation seems to reside in the fact that the first portion of anyhalf cycle of an established alternating current erases the residualmagnetism left in the structure by the preceding half cycle, leaving thestructure momentarily demagnetized. It was also noted that the armature,while humming or buzzing because of its relative lightness, stayed at ornear the unshaded pole, and did not approach the shaded pole. When asufiiciently large restoring spring tension was applied to cause thearmature to approach the shaded pole, it remained there continuously,giving no response to the alternating current. It was further o'bservedthat lower frequencies of alternating: current had no more effect on thedevice in question than direct-current pulses all of one polarity.

I claim:

1. In a quick-acting impulse responsive device, a relatively lightarmature and means rendering it reciprocable between two' positions", anelectromagnet for operating the armature, pole means forone pole of theelectromagnet divided into two branches ending in pole faces so disposedas to exert opposite tractive forces on the armature in directionstoward. the two armature positions respectively-shading means for onebranch delaying flux change therein with respect to flux change in theother branch incident to the rise and to thefall of current in thewinding of the electromagnet responsive to the application andtermination of an impulse of direct current to the winding, meansincluded in the said parts and means for rendering the transientresultant of'the opposite tractive forces capable of moving the armaturefrom one of its positions to the other responsive to each said rise ofcurrent in a series, and rendering it capable of moving the armatureback to its said one position responsive to each said fall of current ofthe series.

2. In a quick-acting impulse-responsive device as set forth in claim 1,means biasing'the armature to move to one of its positions whenmagnetically free to do" so, said transient resultant forc "hen in onedirection acting with the biasl 2 ing means to move the armature to itslast said position, the said transient resultant force when in the otherdirection acting against the biasing means to move the armature to itsopposite position.

3. In a signal system, impulse-responding means for respondingindividually to the impulses of series of direct current impulsesreceived over a pulse-transmission line, said impulse-responding meanscomprising an electromagnet having a winding connected in series withsaid line, an armature operatively associated with the electromagnet,means defining a first position and a second position for the armature,the electromagnet having a main pole member having a pole face sorelated to the armature as to attract the armature to its secondposition responsive to each of said impulses of a series, and means forrestoring said armature from its second position to its first positionresponsive to the cessation of each of the impulses, said restoringmeans including an auxiliary pole member comprising a branch of the mainpole member and having a pole faceso related to the armature as toattract it in opposition to the main pole member,v and a conductingshading member surrounding the auxiliary pole member and delaying fluxchange therein with respect to flux change in the main pole member, andmeans included inthe foregoing whereby the effect of. the restoringmeans is prevented from reaching full value on the receipt of an impulseuntil after the armature has movedfrom its first position toward itssecond position, and means included in the foregoing whereby theeffector the restoring means is continued beyond the end oi. thereceived impulse to restore the armature from its second position to itsfirst position.

4.. In a. signal system according to claim 3, means for applying abiasing force to move the armature to one of its positions when it ismag netically free, the impulse-controlled movement of the armature toits said one position being aidedv by said biasing force, and theimpulsecontrolled movement of the armature to its other positionoccurring. against said biasing force.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 863,667 Struble Aug. 20, 1907 1,158,898 Conrad Nov. 2, 19151,421,269 Lucas June 27', 1922 2,513,400 Carson et al July 4, 1950

